1. Field of the Invention
The present invention relates to an ink composition for a writing instrument and to a writing instrument.
2. Related Background Art
Oil-based inks comprising oil components have conventionally been used as oil-based ball-point pen inks. In recent years, W/O type emulsion inks, having aqueous components dispersed in oil components containing dyes or polar solvents, have been proposed as substitutes for conventional oil-based inks with the aim of improving many properties including smooth writing, thin writing spots, bleeding and blotting. When such W/O type emulsion inks are used to fill writing instruments such as oil-based ball-point pens, they are required to have excellent dispersion stability from the viewpoint of maintaining superior writing properties for prolonged periods.
Japanese Unexamined Patent Publication No. 2007-327003 which will be referred to as “Patent document 1” hereafter, for example, discloses an ink composition for a writing instrument having excellent dispersion stability even when it contains a pigment. Patent document 1 describes adding a pigment to an aqueous component and combining the mixture with an oil component, to obtain an ink composition with droplets comprising a pigment-dispersed aqueous component dispersed in the oil component, the composition being satisfactory in terms of long-term stability, smooth writing, writing density and writing fastness.